Mail transfer agent and Active Directory

[pch0317 <pch0317@gmail.com>]

Hello
I have 150 users in my network. I want to change MsExchange to open MTA.

1. Is there any open MTA which cooperate with Active Directory or
eDirectory? I don't want to create 150 user account. I would like to it
still work even when Active Directory password change (password change
every month).

2. Is there any MTA which have integrated IMAP or POP server? If no,
which IMAP or POP server choose.

Thanks